This invention relates to hydraulic machines including pumps, turbines and reversible pump turbines each having a runner, a runner crown chamber and a runner band chamber and more particularly to a hydraulic balancing apparatus for regulating the axial thrust applied to the runner of such machines.
Hitherto, in hydraulic machines wherein the runner crown chamber is divided by an intermediate or inner seal into an outer runner crown chamber and an inner runner crown chamber, a hydraulic balancing apparatus is known which has balance pipes communicating the outer runner crown chamber with the runner band chamber by opening at their ends in the two chambers in positions which are at the same radial distance from the axis of rotation of the runner, so that a balance can be established between the axial thrust applied to the outer portion of the runner by pressure water in the outer runner crown chamber and the axial thrust applied thereto by pressure water in the runner band chamber by reducing pressure differential between the two chambers so as to thereby reduce the total axial thrust applied to the runner. This type of hydraulic balancing apparatus is disclosed, for example, in a paper by Helmut Winschal entitled "Reversible Pump/Turbine for Racoon Mountain", particularly in FIG. 16 on page 332, reported in the journal of the "INTERNATIONAL CONFERENCE ON PUMPED STORAGE DEVELOPMENT AND ITS ENVIRONMENTAL EFFECTS", pages 322-334,
By using this hydraulic balancing apparatus of the prior art, it is possible to reduce, to a certain degree, the axial thrust applied to the outer portion of the runner. However, since the outer runner crown chamber and the runner band chamber differ from each other in rotational velocity coefficient, the two chambers do not necessarily have the identical radial pressure distribution. This has given rise to the problem of inability of the apparatus to satisfactorily regulate the axial thrust at all times. This problem is important because, in a hydraulic machine of high head and high lift, the outer runner crown chamber and the runner band chamber account for the majority of space of all the pressure chambers and these two chambers have a high hydraulic pressure, with the result that a slight difference in rotational velocity coefficient causes an increase in the value of the axial thrust applied to the runner which increase sometimes may be in the order of several hundred tons.